1. Field of the Invention
The present invention relates to an imaging device for soft x-rays.
2. Description of the Prior Art
There are many types of previously known imaging devices for use with x-rays. For example, imaging devices for hard x-rays, i.e. x-rays having an energy in excess of 30 KeV, are typically used in the medical and manufacturing industries. Such hard x-ray imagers are advantageous since hard x-rays pass essentially without attenuation through air and thus are convenient for medical and certain industrial applications. Hard x-ray imagers, however, only enjoy a resolution of about one-tenth millimeter which, while adequate for most medical applications, is inadequate for many industrial inspection applications.
The previously known imaging devices for hard x-rays, however, have not proven satisfactory as imaging devices for soft x-rays, i.e. x-rays having an energy of less than 20 KeV, for a number of reasons. For example, soft x-rays rapidly attenuate in air and thus are difficult for many applications, such as medical applications, where the x-ray radiation must necessarily pass through air. Also, the image conversion techniques previously used employ conversion techniques from x-ray to visible light that severely lose efficiency for x-ray energies much below 30 keV. This makes them very poor choices for image converters in soft x-ray applications.
There are previously known soft x-ray imaging devices and many of these previously known devices use microchannel plates for converting and multiplying x-rays to electrons. In one such imaging device the microchannel plate was supported by spaced pins and the entire x-ray imager was employed in essentially a complete vacuum. Such a mounting system for the microchannel plate is disadvantageous since the microchannel plate may distort and warp the image. Furthermore, many of these devices must be used in a vacuum and therefore are inappropriate for most industrial applications. These posts must be constructed in matched sets, carefully aligned to the exact distance between the microchannel plate and the baseplate that holds the imaging faceplate. Due to the possibility of a tilt in the faceplate and the baseplate, each post must be constructed for a specific location on a specific imaging unit.
In still another type of x-ray imaging device, the microchannel plate is supported in a housing by thin disks and the housing, in turn, is sealed. These imagers, however, are easily broken and/or become misaligned when subjected to shock. Similarly, the thin disks which mount the microchannel plate to the housing fatigue and sag over time which distorts the image. Furthermore, the atmosphere within the chamber becomes cloudy over time due to outgasing from the parts inside the chamber, and diffusion through the housing which adversely affects the image.
A still further disadvantage of these previously known imaging devices is that, over time, gases entrapped within the microchannel plate leach out into the sealed housing chamber and can damage or otherwise degrade the imaging device.